U.S. Pat. No. 6,299,385 describes the use of a mini jacket for pile installation in an ocean floor. The mini jacket comprises a structural frame with pile sleeves at the corners and a caisson sleeve located within the perimeter of the frame. The mini jacket may be lifted and lowered by sliding its caisson sleeve over a caisson in the form of a tubular pile that has been driven in the ocean floor. In pile installation, piles are driven through the pile sleeves of the mini jacket into the ocean floor.
It is an object of the present invention to provide a method and device of providing a foundation for an elevated mass that is more efficient than the known method, i.e. may require less time than the known method.
According to the invention, this object is achieved by a method comprising:                providing an assembly of a jack-up platform and a framed template, the template having a plurality of interconnected sleeve guide members for receiving the piles, arranged according to the geometric pattern, and means for slidably moving it along the spud poles of the platform,        lowering the framed template along the spud poles from an in-operative position close to the deck of the platform towards the substrate to an operative position; and        driving the piles into the substrate through the sleeve guide members of the template in its operative position.        
The method according to the invention allows providing a foundation in the form of a plurality of piles arranged according to a geometric pattern in less time than known hitherto. After having positioned the jack-up platform in its correct position (in view of the envisaged position of the plurality of piles), it need not be repositioned, as is often required in the known method. Since the template is moved into its operative position by sliding it along the spud poles of the jack-up platform, the template is automatically positioned correctly when the platform is in its correct position. This is very advantageous since positioning a jack-up platform is easily performed by global positioning systems, whereas accurate positioning of structures under water is generally very difficult and expensive. Moreover, since the position of the template is determined by the position of the platform, and the latter is not appreciably influenced by currents and wind forces, this also applies to the template. Also, the use of the template allows to accurately position the plurality of piles in one operation. The operative position of the template corresponds to a position in which the template, and in particular the sleeve guide members thereof, is ready to receive the piles. The operative position preferably corresponds to a position close to the substrate, and even more preferably to a position in which the template substantially rests on the substrate.
Since the position of the template is determined by the position of the (jack-up) platform, and the latter position may be determined with great accuracy, there is no need to check the position of the piles of the foundation afterwards. This saves a significant amount of time and money.
The template may be moved along the spud poles by any means known in the art. It is for instance possible to carry the framed template with a plurality of tension cables attached to it, whereby the cables are varied in length by winches, provided on the platform, and in particular on the work deck thereof. With the aid of the winches, the cables are shortened and/or extended, thereby respectively lifting and/or lowering the template. In a preferred embodiment of the method according to the invention, the means for slidably moving the template along the spud poles of the platform are adapted to level the template such that it is substantially horizontal in its operative position. This may for instance be achieved by at least three; and preferably four cables, from which the template is suspended. More preferably, the winches control the cable lengths independently from each other. The cables are preferably operated by at least three, and preferably four winches. Being able to level the template is in particular useful when the substrate, for instance an under water bottom, is not level itself but shows heights and valleys.
The framed template according to the invention preferably comprises a trussed structure with a plurality of spaced apart sleeve guide members, interconnected by tubular frame members. The template typically has planar dimensions that are larger than the out-of plane dimension, the latter corresponding to a direction parallel to the direction of lifting and lowering of the template. The sleeve guide members are adapted to receive and guide the piles when being driven into the substrate, and preferably comprise cylindrical members, the longitudinal axis thereof extending parallel to the out-of-plane direction of the template. The sleeve guide members are arranged according to a geometric pattern that reflects the desired geometric pattern of the foundation piles. The tubular frame members extending between the sleeve guide members ensure that the sleeve guide members substantially remain in their desired position. In this embodiment, the template is adapted to accommodate a particular geometric pattern of the foundation piles. It is also possible however to make the template geometry adjustable, for instance by providing the template with frame members that are adjustable in length, or by providing the template with nodes that connect frame members and allow to change the angle between the frame members. Such an embodiment allows accommodating different geometric patterns of the foundation piles.
In a preferred embodiment of the method according to the invention, the method comprises locating the position for at least one pile and positioning the assembly of platform and template such that at least one sleeve guide member of the template is above said pile position. Driving a first pile through the at least one sleeve guide member with the template in the operative position fixates the template. In such a position, the sleeve guide members for the other piles will automatically be in their correct positions, due to the fact that their mutual positions are determined by the geometrical layout of the template. This eliminates the need for pile to pile measurements. In yet another preferred embodiment of the method of the invention, the platform is provided with at least one moonpool, adapted to receive a pile, and the assembly of platform and template is positioned such that the moonpool is above said pile position and aligned with one of the sleeve guide members. In such an embodiment, the framed template is at least partly moved over and/or under the jack-up platform thereby covering a substantial part of the platform. Driving a first pile through the moonpool and through said sleeve guide member with the template in the operative position fixates the template with respect to the platform.
Even more preferred is a method, wherein the platform is provided with at least two moonpools, adapted to receive a pile, and the assembly of platform and template is positioned such that the at least two moonpools are above at least two pile positions and aligned with at least two of the sleeve guide members. This embodiment saves even more space, as well as an improved fixation of the template with respect to the platform (and substrate).
Another preferred embodiment of the method according to the invention is characterized in that the framed template is provided to the underside of the platform in its in-operative position, i.e. in its position at rest. Bringing the template from its inoperative position to its operative position (and vice versa) is in this embodiment readily achieved.
The sleeve guide members of the framed template are adapted for receiving and guiding the piles when driving them into the substrate. To be able to receive the piles, the sleeve guide members preferably have a cross-section that is at least the size of the cross-section of the piles. To adequately support the piles, a preferred embodiment of the method makes use of sleeve guide members of which the inner surface is over part of the length of the sleeve guide members provided with supporting ribs for the piles. In order to be able to remove the template easily after the piles have been installed into their final position, the piles are preferably driven into the substrate through the sleeve guide members until the top surface of the piles extends further than said (ribbed) part of the length of the sleeve guide members.
The method according to the invention is preferably characterized in that the piles are driven into the substrate by a pneumatic hammer, provided on the platform. Even more preferred is a method wherein the piles are driven with into the substrate with their top surface further than said (ribbed) part by the follower of a pneumatic hammer. A pneumatic hammer with follower is known per se to the skilled person.
In another aspect of the invention, a method is provided which includes removing the template once the piles have been installed. It is preferred to provide a method wherein removing the template is carried out by lifting it along the spud poles from the operative position towards the in-operative position close to the deck of the platform.
The invention further relates to a method for installing an elevated mass, such as the jacket of a wind mill or a jetty, onto a foundation comprising a plurality of piles that have been driven into a substrate by a method as described above, the method comprising inserting legs of the elevated mass into the piles. Even more preferred is a method, comprising grouting said legs of the elevated mass to the top of the piles.
Although the method according to the invention may be applied to provide a foundation of the type as described above, the method is preferably applied to a substrate that is under water.
In another aspect of the invention, an assembly of a jack-up platform and a framed template, adapted for providing a foundation for an elevated mass, such as the jacket of a wind mill or a jetty, the foundation comprising a plurality of piles, driven into a substrate according to a geometric pattern, is provided, the template having a plurality of interconnected sleeve guide members for receiving the piles, arranged according to the geometric pattern, and means for slidably moving it along the spud poles of the platform. The advantages of such an assembly have already been elucidated in the context of describing the method above, and will not be repeated here.
In another preferred embodiment of the invention, an assembly is provided wherein the platform comprises at least one moonpool, adapted to receive a pile, and aligned with one of the sleeve guide members. In order to be able to receive a pile, the at least one moonpool should have a cross-sectional dimension that is sufficiently large to accommodate a pile. The method according to the invention is particularly suitable for cylindrical hollow piles having an outer diameter of at least 1.2 m, more preferably at least 1.5 m and most preferably at least 1.8 m, and a wall thickness ranging from 0.01 to 0.1 m, more preferably from 0.02 to 0.08 m, and most preferably from 0.04 to 0.06 m. A particularly preferred assembly according to the invention comprises an at least one moonpool that is circular and has a diameter of at least 1.5 m, more preferably of at least 2.5 m and most preferably of at least 3 m.
The method according to the invention is further in particular suitable for cylindrical hollow piles having a length of at least 20 m, more preferably at least 25 m and most preferably at least 30 m, and a weight ranging from 20 to 150 tons, more preferably from 40 to 130 tons, and most preferably from 50 to 110 tons. Another particularly preferred assembly according to the invention comprises sleeve guide members, the height (the dimension in the length direction of the sleeve guide member) of which is at least 1 m, more preferably at least 3 m, and most preferably at least 5 m.
In still another aspect of the invention, a framed template is provided, the template being adapted to provide a foundation for an elevated mass, such as the jacket of a wind mill or a jetty, whereby the foundation comprises a plurality of piles, driven into a substrate according to a geometric pattern, the template comprising a plurality of interconnected sleeve guide members for receiving piles to be driven into the substrate, the sleeve guide members being arranged according to the geometric pattern, and means for slidably moving the framed template along the spud poles of a platform.